The present invention relates to a mixing apparatus.
In a known mixing apparatus, the upper end of the inclined worm is rotatably journalled on the arm of a crank which, in turn, is rotatably journalled in the center of a cover of a conical vessel. In operation of the apparatus, the crank is turned through the center of the cover so that the worm moves along the conical vessel wall. In order to turn the worm about its axis, one of two different drive devices is employed according to the density of the bulk material to be mixed. For the mixing of mixture materials, the density of which is relatively small and is, for example, below 0.7 kilograms per liter, the worm is driven through a Cardan joint arranged at the lower convergent end of the conical vessel. In an apparatus for the mixing of mixture materials, the density of which is greater than 0.7 kilograms per liter, the drive of the worm takes place from above through the interior of the crank.
Both apparatuses have different disadvantages. A disadvantage, which is common to both apparatuses is that the crank, a bearing serving for its journalling and a gear required for its drive are relatively expensive and appreciably increase the manufacturing costs. In order to move the worm along the vessel wall through the mixture stock, in accordance with the properties thereof, very great forces are required in some circumstances. The crank and the bearing serving for its journalling must therefore be very robustly constructed. Since the crank, in the center of the cover, is driven through a shaft and the worm is journalled at the free end of a crank arm forming a long lever arm, great turning moments must be transmitted through the shaft of the crank. The gear, which connects a driving motor to the shaft of the crank, must correspondingly result in a very large step-down ratio and is therefore expensive.
In those apparatuses, in which the drive of the worm takes place through a Cardan joint at the lower vessel end, the joint must constrainedly be arranged on the axis of the vessel. Accordingly, the withdrawal of mixed stock, which likewise takes place at the lower end of the vessel, is made more difficult. The mixed stock can then not be conducted perpendicularly downwards out of the vessel in the center of the lower vessel end, but must be conducted laterally around the Cardan joint. A further disadvantage is that the cardan joint is relatively expensive and moreover liable to trouble, because it has parts contacting the bulk material to be mixed. Furthermore, a shaft feedthrough closing off the interior space of the vessel tightly is required with the Cardan joint.
In those apparatuses in which the drive for the rotation of the worm around its axis takes place through the crank, a shaft must be disposed in the hollow shaft of the crank as well as in the arm of the crank. Both these shafts must be connected to one another through a bevel gear. Furthermore, a bevel gear, which connects the shaft contained in the crank arm with the worm, is however also necessary at the free end of the crank arm. The drive through the crank is thus very complicated and expensive. Moreover, another substantial disadvantage is that the bearing of the worm at the free end of the crank arm, and the bearing of the shafts extending through the crank shaft and the crank arm, as well as the bevel gears generally, require a lubrication. The lubrication points must, however, be sealed off from the free interior space of the mixing vessel because the apparatus is frequently used in chemical processes for the mixing of materials which may not be contaminated by a lubricant. To seal off the lubrication points of the crank, different seals are required, which complicate the construction of the crank still further. In addition, the maintenance, by which the crank must be cleaned and occasionally disassembled, is very time-consuming. A further disadvantage of known apparatuses is that, although the worm is driven through the crank, it is necessary in many cases to journal the worm at its lower end in a ball-and-socket joint. The crank can, in many cases, not be designed to be so rigid and robust and journalled that is suffices to journal the worm at only one end at the crank arm.
German utility model spacification No. 7 420 361, which corresponds to U.S. Pat. No. 3,937,444 discloses a conical mixing apparatus in which the central part of the upper opening of the conical vessel is covered over by a rotatable cover. This is in operating turned by a motor with a spur wheel gear. The lower end of the worm is journalled at the lower end of the vessel by a pivotable ball. The upper end of the worm is connected in the interior of the conical vessel through an articulated connection with a vertical rotatable shaft. The shaft in its turn belongs to a drive unit with a spur wheel gear which itself altogether is rotatable and arranged underneath the cover eccentrically in the interior of the vessel. The drive is connected through a hollow shaft which is conducted through the rotatable cover, and an inner shaft arranged in this with a gear, which is arranged on the outside of the cover and which in operation is driven by the rotary motion of the cover and drives the worm so that this is turned around its own axis and additionally circulates around the mentioned hollow shaft and internal shaft.
With this known apparatus, mixture stock can be filled only into the lower half of the conical vessel or, at best, up to nearly the end of the worm. The space disposed thereover must remain free for the drive unit. As a result, the known apparatus has appreciable overall heights. This in turn acts unfavorably on the manufacturing costs. Furthermore, an apparatus of that kind cannot be used at all in many fields in which high degrees of purity matter. Thus, contact of the substances to be processed with gear parts or the like requiring lubrication is impermissible in the chemical, pharmaceutical or the foodstuffs industries. Furthermore, cleaning of the vessel and the drive unit disposed therein requires a great labor effort. In addition, it would, in that apparatus, be possible only with very great effort to seal off the conical vessel outwardly in gas-tight manner as may be necessary or expedient for certain applications. Further disadvantages also result from the fact that the worm is and must be journalled at the lower end. This journalling can likewise cause contamination of the mixture stock, make the cleaning of the mixer still more expensive and reduces the free cross-sectional area of the outlet during the emptying of the vessel. Furthermore, the complicated gears appreciably increase the manufacturing and maintenance costs.